5' is the increment of movement that provokes an attack that occurs before that 5' movement is completed.
Not true.
Any movement that takes you outside my reach causes an AOO. If you are 4 feet away and move 2 feet that 2-foot move causes an AOO (when the first foot is moved). IF you are 4 feet away and move 1 more foot that does not cause an AOO if you stop then.
No, that's not what I'm suggesting at all. Only that last bit of movement that provokes the OA.
This is exactly what I am saying! You move, only that last bit of that, not the whole 5 feet causes that.
5' is the number. Why? Because any movement less than 5' is abstracted in the rules as remaining in the same space.
To start with it is moving 5 feet away that causes an AOO not "less than" 5 feet away.
Second can you provide a reference suggesting that movement less than 5 feet means you are in the same place?
I agree on both points. What I don't agree on is that you have not moved or that you can take back the movement that happened up until that point.It's a reasonable DM ruling to say that you must finish moving out of reach after the OA resolves. It's also reasonable to say that you don't have to.
I am not saying you have to move out of reach, what I am saying is you have moved to the limit of the reach (in this case 5 feet) and that is how far away you are.